The present invention relates to a power transmission gear for a vehicle of the upper structure swiveling type which has a vehicle body mounted on an undercarriage in such a manner as to be free to swivel.
The conventional power transmission gear for a vehicle of this category, such as a power shovel or the like, is either of the hydraulically driving system type wherein power generated by an engine set in place on a vehicle body is converted into hydraulic pressure and transmitted from a swiveling center to an undercarriage through a swivel joint, with the hydraulic pressure thus transmitted being further converted into power for traveling, or of the mechanically driving system type wherein power generated by an engine set in place on a vehicle is transmitted from a swiveling center to an undercarriage through a bevel gear.
However, in the case of the former systems, a common defect therein has been that conversion of power into hydraulic pressure results in deterioration in efficiency of power transmission, as well as the fact that employment of a hydraulic device is costly, deteriorates reliability and increases durability, and incapability of transmitting a high level of power, hence there is an inherent defect of limitation in terms of the size of a vehicle; while in the case of the latter system, common a defect therein has been that transmission of power from the swiveling center results in an increase in the size of the center swivel joint for controlling travel, an increase in swiveling and sliding resistance, early abrasion of an O-ring, and a drastic limitation on the arrangement of respective apparatuses on the vehicle body. Also, such arrangement of a swivel driving gear and a travel driving gear in an independent and separate manner makes the synchronized operation thereof impracticable.